1. Field of the Invention
This invention relates to a distance measuring device having a transmitter which detects the distance moved by a probe in contact with an object under measurement; the device transmits data representing the distance moved to an external device. More particularly, this invention relates to a distance measuring device with a transmitter characterized by the reducing the power consumption of the transmitter.
2. Description of the Related Art
There have been known various types of distance measuring devices for measuring a minute displacement of an object to be measured. A typical example is a dial gauge of the manually operated portable type. The dial gauge is capable of precisely measuring the displacement of an object up to 0.1 mm or 0.001 mm. Some dial gauges can display the distance of the probe displaced from a reference position in terms of digital figures. In this type of distance measuring device, a core member is coupled with a shaft for supporting the probe. A couple of coils are wound around the core member. These coils are incorporated into a Colpitts oscillator. When the probe is moved, the core member also moves within the couple of coils. The movement causes an oscillating frequency of the oscillator to shift from its reference frequency. This frequency shift is detected. A computing system contained in the measuring device computes the distance moved by the core member, or that by the probe, by using the detected frequency shift. Specifically, an oscillating frequency of the oscillator is counted by a counter, and converted into corresponding digital frequency data. The data obtained is supplied to a controller such as a microcomputer. The microcomputer computes the distance moved by the probe by using the frequency shift represented by that data. The computed data is applied to display, and is digitally displayed.
In the distance measuring device, the exact data cannot be obtained over the entire range of the probe movement, but can be obtained within a specific or effective range of the probe movement.
Another type of distance measuring device is designed with the intention to improve the data processing efficiency of the distance as measured by the manually-operated portable measuring device. In the device, a micro transmitter is built into the distance measuring device of the manually-operated portable type, and the transmitter wirelessly transmits the measured distance to an external host system. The proposed measuring device has a miniature battery assembled thereinto. The battery is for supplying electric power to drive an oscillator, a counter, a controller, a display, the transmitter, and the like. In operation, a power switch is turned on, and those related components are driven. The measuring device computes the distance moved by the probe from a reference position at fixed time intervals, e.g., 0.1 sec., and wirelessly transmits the measured data to the host system. In some such measuring devices, no power switches are used for cost reduction purposes. When loaded with a battery, the device automatically starts and continues the wireless transmission of the moved distance at fixed time intervals.
Most of the electric power is consumed by the transmitter, while the electric power consumed by the remaining circuit components is negligibly small. Even if the electric power is constantly supplied to those remaining components, reduction of the lifetime of battery is of an insignificant degree.
The transmitter output power must be kept at a value exceeding a predetermined value, because the measuring device will frequently encounter a situation where it must transmit the measured data to a distant host system. In such a case, the power consumption by the transmitter considerably increases. Therefore, the battery power is rapidly consumed, and hence its lifetime reduction is considerable.